void cleanVariables(VariablesVectorType& variables)
{
for (unsigned i = variables.size(); i--;) {
Node* node = variables[i];
if (!node)
continue;
if (node->op() != Phantom && node->shouldGenerate())
continue;
if (node->op() == GetLocal) {
node = node->child1().node();
// FIXME: In the case that the variable is captured, we really want to be able
// to replace the variable-at-tail with the last use of the variable in the same
// way that CPS rethreading would do. The child of the GetLocal isn't necessarily
// the same as what CPS rethreading would do. For example, we may have:
//
// a: SetLocal(...) // live
// b: GetLocal(@a) // live
// c: GetLocal(@a) // dead
//
// When killing @c, the code below will set the variable-at-tail to @a, while CPS
// rethreading would have set @b. This is a benign bug, since all clients of CPS
// only use the variable-at-tail of captured variables to get the
// VariableAccessData and observe that it is in fact captured. But, this feels
// like it could cause bugs in the future.
//
// It's tempting to just dethread and then invoke CPS rethreading, but CPS
// rethreading fails to preserve exact ref-counts. So we would need a fixpoint.
// It's probably the case that this fixpoint will be guaranteed to converge after
// the second iteration (i.e. the second run of DCE will not kill anything and so
// will not need to dethread), but for now the safest approach is probably just to
// allow for this tiny bit of sloppiness.
//
// Another possible solution would be to simply say that DCE dethreads but then
// we never rethread before going to the backend. That feels intuitively right
// because it's unlikely that any of the phases after DCE in the backend rely on
// ThreadedCPS.
//
// https://bugs.webkit.org/show_bug.cgi?id=130115
ASSERT(
node->op() == Phi || node->op() == SetArgument
|| node->variableAccessData()->isCaptured());
if (node->shouldGenerate()) {
variables[i] = node;
continue;
}
}
variables[i] = 0;
}
}
void cleanVariables(VariablesVectorType& variables)
{
for (unsigned i = variables.size(); i--;) {
Node* node = variables[i];
if (!node)
continue;
if (node->op() != Phantom && node->shouldGenerate())
continue;
if (node->op() == GetLocal) {
node = node->child1().node();
ASSERT(node->op() == Phi);
if (node->shouldGenerate()) {
variables[i] = node;
continue;
}
}
variables[i] = 0;
}
}
